1. Field of the Invention
The present invention relates to a scan type radar device, particularly to an on-vehicle scan type radar device for detecting a target by a beat signal obtained by mixing a transmitted signal with a received signal which is a frequency modulation signal of the transmission signal reflected from an objective such as a car or a stationary objective (hereinafter referred to as a target), wherein the target is accurately acquired by forecasting a detected value to be obtained at this time from a detected value obtained at a preceding time even though the target detected at the front of a host vehicle moves in the lateral direction.
2. Description of the Related Art
Recently, car crash accidents are liable to increase due to a distraction of attention caused by long and monotonous driving, on a highway, of a vehicle. Also, there is a requirement for the automatic running of a vehicle not only at a constant speed by means of a constant speed driving device but also while tracking a preceding vehicle running at the front of a host vehicle.
Under such circumstances, an on-vehicle radar device has been put into practice, which always measures a distance from the preceding vehicle and automatically reduces the running speed of the host vehicle or brakes the host vehicle if the degree of reduction of the distance becomes large, to prevent a car crash, or always monitors positions of a plurality of preceding vehicles to enable the host vehicle to carry out automatic driving.
Such an on-vehicle radar device generally includes an FM-CW (frequency-modulated continuous wave) radar or a pulse drive radar. Among them, the FM-CW radar device provides a base band signal whose frequency changes like a sawtooth waveform (a triangular wave) to a transmission voltage controlled oscillator (VCO), then transmitted forward of the host vehicle from an antenna after being frequency-modulated, receives the signal reflected from a target such as the preceding vehicle by the antenna and mixes the transmitted signal and the received signal to result in a beat signal from which the preceding target is detected.
In this case, the transmitted signal is transmitted as a plurality of beams spaced at a predetermined angle by oscillating (scanning) the antenna in a predetermined angular range forward of the host vehicle. When the lateral position of the target at the front of the host vehicle is detected by using this on-vehicle scan type radar device, in general, peaks of the received signal in the respective beams are gathered to obtain groups of peaks and the lateral position of the one or more targets are calculated based on the maximum peak in each group.
However, there are drawbacks in the above-mentioned scan type on-vehicle radar device as follows:
(1) When two targets are at the front of the host vehicle and positioned side by side in the lateral direction or overlapped with a stationary objective such as a guard rail in the lateral direction, a position of the maximum peak may fluctuate largely. It the lateral position of the target fluctuates largely as described above, the identification of the position of the target becomes difficult and the target may be lost.
(2) When the host vehicle carrying the radar changes its position, for, example, by changing a traffic lane, the lateral position of the target fluctuates largely to cause a loss of continuity in a system wherein the continuity is obtained by tracking data of the target obtained at this time from the past data of the target because the reference value for determining the continuity is definite whereby if the fluctuation exceeds this reference value, the continuity is lost.
(3) When the peak representing the target is overlapped with a stationary objective such as a guard rail or the peak fluctuates in the lateral direction by a multiple reflection from a concrete wall or the like, there may be a case in which the lateral position of the target is outside of the guard rail or the concrete wall to lose the position of the preceding vehicle.
(4) When there is a stationary objective widely spread in the lateral direction at the front of the host vehicle, such as an overbridge, data signal of the target is combined by data signal of the overbridge as if the lateral position of the target largely fluctuates, which may cause the target to be lost.
Also, there are the following problems:
(5) In the FM-CW radar device, pairing is carried out by extracting the respective peaks in the up-beat (beat generated by the mixture of the transmitted beam and the reflected beam when the frequency of the transmitted beam is increasing) and down-beat (beat generated by the mixture of the transmitted beam and the reflected beam when the frequency of the transmitted beam is decreasing) corresponding to each other. If there are a lot of peaks in the same angular direction, the pairing may be carried out between invalid peaks to miss the target.
(6) When the detected target is positioned adjacent to a more reflective target in the lateral direction (angular direction), only one group of peaks is formed in the angular direction whereby the actual peak of the preceding vehicle is embedded in a powerful peak of the other large target and the detection of the peak of the preceding vehicle becomes impossible. As result, the continuity of the target cannot be detected.
(7) When the detected target is positioned adjacent to a more reflective target in the distance direction (frequency changing direction of the rador device), only one group of peaks is formed in the frequency changing direction whereby the actual peak of the preceding vehicle is embedded in a powerful peak of the other large target and the detection of the peak of the preceding vehicle becomes impossible to lose the continuity of the target.
(8) when a target to be detected is a less reflective object such as a motor cycle, a peak is lower than a threshold value of detection to lose the target.
(9) while a correspondence is made between the respective peaks of the up-beat and the down-beat in a certain angular range, in some cases, an invalid pairing is made when the peaks of different objects are detected at the same frequency.
A first object of the present invention is to solve the problems in the above-mentioned on-vehicle radar device in the prior art and provide a scan type radar device capable of assuredly acquiring the preceding target and detecting the lateral position thereof even though the peak representing the lateral position of the target detected by a plurality of beams irregularly fluctuates in the lateral direction.
A second object of the present invention is to solve the problems in the above-mentioned on-vehicle radar device in the prior art and provide a scan type radar device having a lower risk of mis-pairing, wherein regarding a target previously detected, the position of the target at this time is estimated by the position thereof at the preceding time, and a representative peak is calculated by executing the grouping with the forecast position as a center.
The scan type radar device for achieving the first object is defined by the first to ninth aspects described below.
The first aspect is a radar device for detecting a target by receiving a returned signal reflected from the target, having a reference value of the lateral fluctuation of the target for judging the continuity between past-detected target data and that detected at this time, characterized in that means is provided for changing the reference value in accordance with the movement of the detected target.
The second aspect is a modification of the first aspect that the reference value changing means comprises means for detecting the lateral fluctuation of the target between the past-detected target data and that detected at this time and means for changing the reference value if it is judged that the target moves to exceed the reference value.
The third aspect is a modification of the second aspect that the reference value changing means forms the judgement that the target moves while exceeding the reference value when all the lateral movements show generally identical values exceeding the reference value.
The fourth aspect is a modification of the first aspect by means for detecting the lateral fluctuation of the target between the past-detected target data and that detected at this time and means for restricting the lateral fluctuation of a specific target by a predetermined restriction value when the fluctuation exceeding the reference value occurs in data of the specific target while the fluctuation of other target data is within the reference value.
The fifth aspect is a radar device of the first aspect capable of detecting a stationary objective, characterized by means for detecting the lateral fluctuation of the target between the past-detected target data and that detected at this time, means for setting a road edge line of a road at the front of a vehicle from the detected stationary objective, and means for correcting the lateral fluctuation of the specific target by the road edge line when the fluctuation exceeding the road side line occurs in data of the specific target.
The sixth aspect is a modification of the fifth aspect that the road edge setting means sets the road side line by using the target judged as the stationary objective within a certain reference distance from the host vehicle.
The seventh aspect is a modification of the fifth or sixth aspect that the road side setting means sets the road side line by using a curve information of the road calculated by means for calculating a curve information of the curved road at the front of the host vehicle.
The eighth aspect is a radar device of the first aspect capable of detecting a stationary objective, characterized by means for detecting the lateral fluctuation of the target between the past-detected target data and that detected at this time, means for judging that the target is a specific stationary objective when the target data widely spreads in the lateral direction, and means for limiting the lateral fluctuation of a predetermined target data by a predetermined limit value when the predetermined target data is overlapped with the predetermined stationary objective data.
The ninth aspect is a radar device of the first aspect for transmitting a plurality of beams, receiving a predetermined number of beams reflected from the target and detecting the target from peaks of a predetermined number of beat signals obtained by mixing the transmission signal with the reception signal, characterized by means for detecting the lateral fluctuation of the target between the past-detected target data and that detected at this time and means for limiting the lateral fluctuation of the past target data at this time by a predetermined limit value.
The tenth aspect is a modification of the first aspect that the radar device is an on-vehicle radar device using a millimetric wave. In this regard, any combinations of these first to tenth aspects, of course, constitute the present invention.
The eleventh aspect is a radar device for achieving the above-mentioned second object is a radar device for detecting a target by a beat signal obtained by transmitting a frequency-modulated signal, receiving a signal reflected from the target and mixing these transmission signal and the reception signal, wherein a representative peak is calculated by grouping peak data in an up-beat and a down-beat, respectively, by a grouping means and the target is detected by pairing the representative peaks in the respective grouped beats by a pairing means, characterized in that means for forecasting a representative peak position at this time in both of the up-beat and the down-beat from peak position data at the preceding time, to every target obtained by the pairing, and past-correspondence grouping means for carrying out the grouping in the up-beat and the down-beat in the vicinity of the forecast representative peak position at this time are provided so that the pairing means carries out the pairing by using the representative peaks calculated by the past-correspondence grouping means,
The twelfth to twenty-eighth aspects are possible in the present invention.
A twelfth aspect is a modification of the eleventh aspect that the past-correspondence grouping means carries out the grouping of the peak data in the up-beat and the down-beat discrete in the frequency and angular directions, around the representative peak at this time, if any, forecast by the peak position forecasting means, and grouping of the remaining peak data thereafter.
A thirteenth aspect is a modification of the twelfth aspect that when the representative peak at this time is calculated by the past-correspondence grouping means in either one of the up-beat and the down-beat in the vicinity of the forecast position and a peak is detected in the vicinity of the forecast position in the other beat as well as a larger peak is detected at a position shifted in the angular or frequency direction, the past-correspondence means judges that a peak is not embedded in other target in one beat but is judged that a peak is embedded in other target in the other beat.
A fourteenth aspect is a modification of the thirteenth aspect that when a level of the peak in the other beat shifted in the angular or frequency direction from the forecast position is larger than a level of the representative peak at this time in the vicinity of the forecast position in the one beat, the past-correspondence grouping means carries out the past-correspondence grouping process.
A fifteenth aspect is a modification of the thirteenth or fourteenth aspect that the past-correspondence grouping means makes an angle or frequency of a peak calculated as the representative peak in the past-correspondence grouping process to be equal to the angle of the representative peak at this time calculated in the beat judged to be not embedded.
A sixteenth aspect is a modification of the thirteenth aspect that when the past-correspondence grouping means carried out the retrieval of a peak in the other beat larger than the peak detected in the vicinity of the forecast position in the direction shifted in the frequency direction, the frequency retrieval range is variable in accordance with the difference in power between this peak and the representative peak calculated in the one beat.
A seventeenth aspect is a modification of the sixteen aspect that means for measuring a reflection level of the reflected signal is provided and when the reflection level of the reception signal in one beat is higher than the reflection level of the reception signal in the other beat, the past-correspondence grouping means carries out the past-correspondence grouping process.
A eighteenth aspect is a modification of the seventeenth aspect that when an absolute value of the reflection level of a larger peak detected in the direction shifted in the frequency direction relative to a peak detected in the vicinity of the forecast position exceeds a predetermined threshold value, the past-correspondence grouping means carries out the past-correspondence grouping process.
A nineteenth aspect is a modification of the seventeenth or eighteenth aspect that the past-correspondence grouping means makes an angle of the peak calculated as a representative peak in the past-correspondence grouping process to be equal to an angle of a representative peak calculated at this time in one beat.
A twentieth aspect is a modification of the seventeenth or eighteenth aspect that the past-correspondence grouping means maintains an angle of the representative peak at the preceding time and uses as an angle of a peak to be calculated as a representative peak in the past-correspondence grouping process.
A 21st aspect is a modification of the twelfth aspect that when a peak having a smaller power corresponding to a representative peak at this time is detected in the vicinity of the forecast position in either one of up-beat and down-beat by the past-correspondence grouping means, but no peak is detected in the vicinity of the forecast position in the other beat, the past-correspondence grouping means carries out an imaginary grouping process for calculating an imaginary representative peak at the same position in the other beat as that of a representative peak in the one beat, and the pairing means carries out the pairing by using the representative peak and the imaginary representative peak calculated by the past-correspondence grouping means.
A 22nd aspect is a modification of the 21st aspect that the past-correspondence grouping means carries out the imaginary grouping process solely when the position of the peak having a small power is within a predetermined range at the front of the vehicle.
A 23rd aspect is a modification of the 21st aspect that the past-correspondence grouping means carries out the imaginary grouping process when the position of the peak having a small power completely coincides with the forecast value at this time.
A 24th aspect is a modification of the twelfth aspect that when the representative peak at this time is calculated at a position completely coinciding with the forecast position in the beat in either one of the up-beat and the down-beat by the past-correspondence grouping means, the pairing means carries out the pairing by solely using the completely coincided peak in the one beat at this time irrespective of the result of the grouping by the past-correspondence grouping means in both of the beats.
A 25th aspect is a modification of the twelfth aspect that when there is the difference exceeding a reference value in the angular direction or the frequency direction between the representative peak at this time calculated in the vicinity of the forecast position in one of the up-beat and the down-beat and the representative peak at this time calculated in the vicinity of the forecast position in the other beat, the pairing means removes the both from the pairing objects.
A 26th aspect is a modification of the twelfth aspect that when the representative peak at this time is calculated in the vicinity of the forecast position in either one of the up-beat and the down-beat by the past-correspondence grouping means and a peak is detected at a position shifted from the forecast position in the angular or frequency direction in the other beat but not detected in the vicinity of the forecast position, the pairing means removes the representative beat at this time from the pairing object.
A 27th aspect is a modification of the twelfth aspect that when the calculation of the representative peak at this time in the vicinity of the forecast position by the past-correspondence grouping means is interrupted, the past-correspondence grouping means repeats the calculation of the representative peak at this time in the vicinity of the forecast position a predetermined times.
A 28th aspect is a modification of the twelfth or 27th aspect that when the calculation of the representative peak at this time in the vicinity of the forecast position by the past-correspondence grouping means is interrupted, the past-correspondence grouping means calculates the representative peak at this time by widening a range in the vicinity of the forecast position in the angular or frequency direction in accordance with a length of the interrupted time.
According to the above-mentioned first to ninth aspects and the possible combinations thereof, the following actions are obtained:
(1) Even if two targets running at the front of the host vehicle are arranged side-by-side or overlapped with a peak of the stationary objective such as a guard rail in the lateral direction, it is possible to identify a position of the target and not to lose the target.
(2) Even if the host vehicle changes a position thereof, for example, by changing traffic lanes, since the reference value for judging the target is changed so that the continuity of the target is obtained, the target is not lost.
(3) Even if the peak of the target is overlapped with the peak of the stationary objective such as a guard rail or the peak is shifted in the lateral direction caused by the multiple-reflection from a concrete wall or others, the position of the preceding vehicle is not missed.
(4) Even if a stationary objective widely spread in the lateral direction such as an overbridge exists at the front of the vehicle, the target is not missed.
Also, according to the above-mentioned eleventh to 28th aspects and the possible combinations thereof, the following actions are obtained:
(5) Regarding the target detected once by the pairing when a number of peaks exist in the same frequency direction and judged that the existence thereof is certainly reliable, the pairing is carried out after the position of the target at this time is forecast from the preceding position and the grouping around the forecast position is carried out, whereby it is possible to suppress the generation of the mis-pairing.
(6) Even if the peak of the preceding target is embedded in the peak of the other large target in the angular direction, it is possible to judge the continuity of the target since the judgement is made that the target exists, if the present correspondence of the peak of the preceding target is judged from the past data in the up-beat or the down-beat.
(7) Even if the peak of the preceding target is embedded in the peak of the other large target in the frequency direction, it is possible to judge the continuity of the target as the judgement is made that the target exists, if the present correspondence of the peak of the preceding target is judged from the past data in the up-beat or the down-beat.
(8) Even if the target is small and the reflection thereof is also small, the possibility for losing the target is reduced because it is judged that the target exists if the present correspondence of the peak of the preceding target in either one of the up-beat and the down-beat is can be taken.
(9) Since the judgement is finally made that whether or not it is the same target from the arrangement of the peaks when the correspondence between the respective peaks in the up-beat and the down-beat is judged, it is possible to reduce the possibility of mis-pairing of different objectives.